Method of making zirconium oxide



Feb. 25, 1941.

c. J. KINZIE r-:T AL Re- 21,726 METHOD OF MAKING ZIRCONIUM XIDE Original Filed Sept. 2, 1935 2 Sheets-Sheet l y marc-R IN V EN TOR.

I ATTORNEY Feb. 2 5, 1941. i c, J, KINzlE HAL Re. 21,726 fi METHOD OF MAKING' ZIRCONIUM OXIDE Original Filed Sept. 2, 1936 2 Sheets-Sheet 2 Z/RCON CHRBON M/X v INVENToR. CoH/QSE COKE CHHRLES J K//vz/E DONALD H E A TTORNE Y Reissued Feb. 25, 1941 UNITED STATES PATENT OFFICE METHD OF MAKING ZIRCONIUM OXIDE corporation of Maine Original No.

2,168,603, dated August 8, 1939, Se-

rial No. 99,030, September 2, 1936. Application for reissue October 11, 1940, Serial No. 360,854

11 Claims.

Our invention relates to the production of an improved anhydrous crystalline zirconium oxide, more particularly a new crystalline zirconium oxide of a high degree of purity and of exceptionally uniform particle size and other advantageous properties, in the electric resistance furnace with the incidental production of silicon carbide as a byproduct of the Waste heat of the reaction.

The accompanying drawings show a type of an electric resistance furnace in which our invention may be practiced.

Fig. 1 is a sectional elevation of the furnace and its contents;

Fig. 2 is a horizontal section taken on the line 2-2 of Fig. l;

Fig. 3 is an enlarged section of what is illustrated in Fig. 2 to show a preferred method of loading;

Fig. 4 is an enlarged horizontal section of what is illustrated in Fig. 1 to show a preferred method of loading; and

Fig. 5 is an enlarged detail vertical section showing a modified method of loading the saggers.

Referring to these Figs. 1 and 2, the hearth of any suitable material is supported on piers, the hearth forming a supporting base for the furnace and its charge. Such base has also side and end Walls to hold the charge. Through each of the end Walls is a suitable opening for arranging the graphite electrodes, While the sidewalls of the furnace are built up of loose bricks to permit the free escape of evolved gases.

Outside the furnace the ends of the graphite electrodes may be cooled by passing a current of water through them as shown in Figs. 1 and 2.

Extensive researches covering many variations in proportions, treatment in furnace, etc., have led us to the following conclusions:

A. That zirconium silicate (ZrSiOi) in proper admixture with carbon could be made to yield an essentially silicon-free zirconium compound from which free separate crystals of ZrOz of the desired particle size could be made, and that by processing according to either of our alternative methods, the silicon carbide could be made to separate from the zirconium compound.

B. An important part of our improved methods is in our relatively ne carbon (petroleum coke) -80 mesh, that is, intimately mixed with the granules of ZrSiO4, most of which were also in size -80 mesh since the carbon and zircon when treated should be of about the same particle size. l

C. Another important feature of our invention is the proportion of petroleum coke to zircon. 25 parts by Weight of 80 mesh petroleum 5 coke to 100 parts by weight of zircon is preferred. We have found that if much less coke is used, there is formed in proportion to the lowered coke content an increasing amount of zirconium oxide in the form of undesirable large crystals, more or less like synthetic baddeleyite. For example, a mixture of 100 parts of zircon and 18 parts of coke Will show very denite amounts oi synthetic baddeleyite aggregates on the screen along With SiC aggregates. Such forlnation is usually undesired, since synthetic baddeleyite is not particularly suitable for subsequent processing to form an opacifier for vitreous enamels, even if it could be separated from the 20 SiC. On the other hand, if the amount of iine coke is increased, the surplusage is consumed to form SiC in small separate crystals which can not be readily separated from the desired zirconium compound.

D. Our discovery that by adding to the mixture of 100 parts of Zircon and 25 parts of fine coke, parts of petroleum coke between and 1/4" in size, preferably 1/8", these `coke pieces serve as absorbing zones for the silicon compound which completely leaves the zirconium. The silicon forms silicon carbide crystals as aggregates, which remain more or less of the original coarse coke size. It is thus possible by coarse sieving initially to remove most of the SiC from the zirconium compound.

E. By sieving to mesh the sagger discharge, the zirconium-carbon complex is almost completely separated from the SiC, the latter remaining on the sieve. Since the zirconium 40 compound iormed'must be ultimately calcined in an oxidizing atmosphere to ZrOz, such calcination may be done by heating the entire discharge derived from saggers. The granular zirconium-carbon compound is thereby converted to the desired ZrOz product, While the SiC remains unaltered in the form of relatively large crystals, and may be removed by any suitable means, such as screening, flotation, taining, air separation; We have used sieving with good success.

F. T'he temperature in the charge during the electric resistance furnace operation should be kept Well below the decomposition point of the silicon carbide. We have found that a tempera- C. is best, preferably ture between 1800-2000 around 1800 C., or as 10W as possible in order to produce the desired ZrOz product. If the temperature goes too high, fully formed Zirconium carbide results, which yields undesired large crystals of Zr02 upon calcination.

G. Where a ZrOz containing very small amounts of SiC vis desired, We have found that such product may be produced by first placing a layer of 1/8 coke inside the sagger Walls, and then insertingtherein the 100:25 mix of -80 mesh Zircon and mesh coke followed by heating, etc. In this Way the SiC forms an inner Wall in the sagger due to the fact that the silicon completely leaves the Zr Zone, and the granular zirconium compound is easily removed and -calcined to a cream white product with but a trace of SiC. For practical reasons of operation we prefer the rst method, since it yields commercially practical results with less work.

The following examples will show how our improved methodsmay be practiced to obtain our novel and improved anhydrous crystalline zirconium oxide:

Example 1 Percent Fixed carbon -90 Volatile matter 8 Ash 0.25

This coke is ground so as to pass an E10-mesh sieve.

A mixture is then made consisting of:

Parts by weight Zirconium silicate '1009 Petroleum coke 80 mesh 25 To this mixture are added 25 parts by weight of coarse petroleum coke $6 to 1/4", but preferably as close to 1/8" size as possible, and the whole charge is intimately mixed. Each of the three carbon saggers shown in Figs. 1 and 2 is filled with the charge, and then placed in the core of theresistance furnace as illustrated in Figs. 1 and 2.

The power input, period of the run, etc., will of course vary with the size of the saggers, furnace type, etc., but the temperature and time under heat should be such as only to decompose the Zircon, convert its zirconium into a. Zirconium-carbon-oxygen complex, and allow the silicon compounds to be fully converted to silicon carbide by absorption within the coarse carbon pieces. But We avoid such as excess of heat or its duration as would tend to fully form zirconium carbide.`

Under these described conditions, the charge upon cooling will consist of two phases-one a zirconium-carbon-oxygen compound or coher ent granular zirconiumv carboxide and aggregates of SiC crystals in the places where pieces of 'coarse coke were formerly located.

By screening the cooled sagger discharge through a 40 mesh sieve, two portions were obtained composed substantially of The 70% 40 mesh zirconium compound contained approximately:

. Per cent Zr 79.00 Tir 0.01 SiC 2.00 Fe 0.011 C 10.0 Oxygen 8.98

The 30% SiC plus C would actually contain about its weight of SiC, as some surplus of carbon is desirable. From this product crystals of SiC' may be obtained by igniting to oxidize the free carbon, crushing, washing, etc., to produce grains of SiC.

The improved zirconium oxide is produced from the -40 mesh zirconium compound product by ignition in air and cooling. This product is a. fairly clean cream-white powder. By feeding the powder into a stream of air and collecting in a dust chamber, any loose aggregates are freed, and the resulting product may then be obtained by suitable lawning (-325 mesh) or by any suitable gravity separation method, air classification, iioatation, etc., so as to be essentially free of SiC.

Typical zirconium oxide products thus produced contain approximately:

, Per cent ZrOz-tadsorbed gas 98.80 T102 0.02 F6203 0.01 SiC 0.40 A1203 Y 0.30 Rare earths 0.20 Others 0.27

Example 2 -This procedure diiTers from Example 1 only to the extent that inside each sagger is placed a cylinder of thin paper as shown in Fig. 5, just strong enough to support a 7%" layer of le petroleum coke inside the sagger wall. With the paper in'place and the coarse coke charged, the mixture of parts Zircon sand and 25 parts -80 mesh coke is then arranged to iill the space inside the paper cylinder. The carbon covers are'put on and the three saggers are then placed in the core of the furnace and the run made as in Example 1.

The granular zirconium c-arboxide may then be removed entirely free from the SiC which now has been formed as a lining. The zirconium carboxide compound upon calcination yields a pure ZrOz which under best conditions is free of SiC, without recourse to lawning. The SiC is then readily detached from the sagger and any free carbon removed by ignition and the SiC may be recovered.

We claim:

1. 'I'he method of making anhydrous crystalline zirconium oxide from zirconium silicate or Zircon, which comprises placing a mixture of suicient size to serve as nuclei for particles of silicon carbide formed, Within a carbon container surrounded by resistance carbon acting substantially as the heat-producing resistor, but substantially mechanically separated therefrom, and then heating said separated charge in an electric resistance furnace by temperatures mainly developed in the resistor surrounding the charge without fusion, but With substantial decomposition of the charge, to yield a separable mixture of an essentially silicon-free zirconiumcarbon-oxygen complex and separable silicon carbide crystal aggregates absorbed Within the larger particles of coarse coke.

2. The method of making anhydrous crystalline zirconium oxide from zirconium silicate or zirco-n, which comprises placing a mixture of nely-divided zircon and finely-divided carbon in proportions of about 4 to l and of substantially the same particle size, together with larger particles of coarse coke of sufficient size to serve as nuclei for particles o-f solicon carbide formed, Within a carbon container surrounded by resistance carbon acting substantially as the heat-producing resistor, but substantially mechanically separated therefrom, and then heating said separated charge in an electric resistance furnace by temperatures mainly developed in the resistor surrounding the charge Without fusion, but with substantial decomposition of the charge, to yield a separable mixture of an essentially silicon-free zirconium-carbon-oxygen complex and separable silicon carbide crystal aggregates absorbed Within the larger particles of coarse coke.

3. The method of making anhydrous crystalline zirconium oxide from zirconium silicate or zircon, which comprises placing a mixture of nely-divided zircon and finely-divided carbon in proportions of about 4 to 1 and of substantially the same particle size, together with larger in proportions of about 4 of zircon to 1 of coke,

Within a carbon container surrounded by resistance carbon acting substantially as the heatproducing resistor, but substantially mechanically separated therefrom, and then heating said separated charge in an electric resistance furnace by temperatures mainly developed in the resistor surrounding the charge Without fusion, but with substantial decomposition of the charge, to yield a separable mixture of an essentially siliconfree zirconium-carbon-oxygen complex and separable silicon carbide crystal aggregates absorbed Within the larger particles of coarse coke.

4. The method of making anhydrous crystalline zirconium oxide from zirconium silicate or zircon, which comprises placing a mixture of finely-divided zircon and finely-divided carbon, in which mixture are contained larger particles of coarse coke, Within a carbon container surround- A ed by resistance carbon acting substantially as the heat-producing resistor, but substantially mechanically separated therefrom, then heating said separated charge in an electric resistance furnace by the temperatures mainly developed in the resistor surrounding the charge Without fusion, but with substantial decomposition of the charge, to yield an essentially silicon-free zirconium-carbon-oxygen complex and separable silicon carbide crystal aggregates, calcining the mass under oxidizing conditions to produce said zirconium oxide, and then separating the silicon carbide crystal aggregates from the zirconium oxide.

5. The method of making anhydrous crystalline zirconium oxide from zirconium silicate or zircon, which comprises placing a mixture of iinely-divided zircon and finely-divided carbon of substantially the same particle size, in which mixture are contained larger particles of -coarse coke, Within a carbon container surrounded by resistance carbon acting substantially as the heat-producing resistor, but substantially mechanically separated therefrom, then heating said separated charge in an electric resistance furnace by the temperatures mainly developed in the resistor surrounding the charge without fusion, but with substantial decomposition of the charge, to yield an essentially silicon-free zirconium-carbon-oxygen complex and separable silicon carbide crystal aggregates, calcining the mass under oxidizing conditions to produce said zirconium oxide, and then separating the silicon carbide crystal aggregates from the zirconium oxide.

6. The method of making anhydrous crystalline zirconium oxide from zirconium silicate or zircon, which comprises placing a mixture of finely-divided zircon and finely-divided carbon in proportions of about 4 to 1, in which mixture are contained largerparticles of coarse coke, Within a carbon container surrounded by resistance carbon acting substantially as the heatproducing resistor, but substantially mechanically separated therefrom, then heating said separated charge in an electric resistance furnace by the temperatures mainly developed in the resistor surrounding the charge Without fusion, but with substantial decomposition of the charge-to yield an essentially silicon-free zirconium-carbon-oxygen complex-and separable silicon carbide crystal aggregates, calcining the mass under oxidizing conditions to produce said zirconium oxide, and then separating the silicon carbide crystal aggregates from the zirconium oxide.

7. The method of making anhydrous crystalline zirconium oxide from zirconium silicate or zircon, which comprises placing an intimate mixture of finely-divided zircon and finely-divided carbon in proportions of about 4 to 1 and of substantially the same particle size, in which mixture are contained larger particles of coarse coke, within a carbon container surrounded by resistance carbon acting substantially as the heat-producing resistor, but substantially mechanically separated therefrom, then heating said separated charge in an electric resistance furnace by the temperatures mainly developed in the resistor surrounding the charge Without fusion, but with substantial decomposition of the charge, to yield an essentially silicon-free zirconium-carbon-oxygen complex and separable silicon carbide crystal aggregates, calcining the mass unde-r oxidizing conditions to produce said zirconium oxide, and then separating the silicon carbide crystal aggregates from the zirconium oxide.

8. The method of making anhydrous crystalline zirconium oxide from zirconium silicate or zircon, Which comprises placing an intimate mixture of finely-divided Zircon and nely-divided carbon in proportions of about 4 to 1, mixed with particles of coarser coke in the proportion of zircon to coarser coke of about 4 to l, Within a carbon container surrounded by resistance carbon acting substantially as the heat-producing resistor, but substantially mechanically separated therefrom, then heating said separated charge in an electric resi-stance furnace by the temperatures mainly developed in the resistor surrounding the charge without fusion, but with substantial decomposition of the charge, to yield an` essentially silicon-free zirconium-carbonoxygen complex and separable silicon carbide crystal aggregates, calcining the mass under oxdizing conditions to produce said zirconium oxide, and then separating the silicon carbide crystal aggregates from the zirconium oxide.

9. The method of making anhydrous crystalline zirconium oxide from zirconium silicate or zircon, which comprises placing a mixture of finely-divided Zircon and finely-divided carbon in proportions of about 4 to 1, in which mixture are` contained larger particles of coarse coke, Within a carbon container surrounded by resistvance carbon acting substantially as the heatproducing resistor, but substantially mechanically separated therefrom, then heating said separated charge in an electric resistance furnace between 1800 and 2000 C. by heat mainly developed in the resistor surrounding the charge without fusion, but with substantial decomposition of the charge, to yield an essentially siliconfree zirconium-carbon-oxygen complex and separable silicon carbide crystal aggregates, calcining the mass under oxidizing conditions to produce said zirconium oxide, and then separating the silicon carbide crystal aggregates from the zirconium oxide.

10. The method of making anhydrous crystalline zirconium oxide from zirconium silicate or Zircon, which comprises placing a mixture of finely-divided Zircon and finely-divided carbon, together with larger particles' of coarse coke,

L Within a carbon container surrounded by resistance carbon acting substantially as the heatproducing resistor, but substantially mechanically separated therefrom, then heating said separated charge in an electric resistance furnace by the temperatures mainly developed in the resistor surrounding the charge Without fusion, but with substantial decomposition of the charge, to yield an essentially silicon-free zirconium-carbon-oxygen complex and separable silicon canbide crystal aggregates, separating the silicon carbide crystal aggregates from the said zirconium-carbon-oxygen complex, and calcining the latter under oxidizing conditions to produce said anhydrous crystalline zirconium oxide.

1l. 'I'he method of making anhydrous crystalline zirconium oxide from zirconium silicate or Zircon, Which comprises placing an intimate mixture of finely-divided Zircon and finely-divided carbon in proportions of about 4 to l and of substantially the same particle size, in which mixture are contained larger particles of coarse coke, Within a carbon container surrounded by resistance carbon acting substantially as the heat-producing resistor, but substantially mechanically separated therefrom, then heating said separated charge in an electric resistance furnace by the temperatures mainly developed in the resistor surrounding the charge without fusion, but with substantial decomposition of the charge, to yield an essentially silicon-free Zirconium-carbon-Oxygen complex and separable silicon carbide crystal aggregates, separating the silicon carbide crystal aggregates from the said Zirconium-carbon-oxygen complex, and calcining the latter under oxidizing conditions to produce said anhydrous crystalline zirconium oxide.

CHARLES J. VKINZIE. DONALD S. HAKE. 

